The present invention relates to the elimination of unwanted materials from a gas flow line, such as materials generated in or present as unreacted process additives in low pressure fabrication processes. In such low pressure processes, an effluent is removed from the process reaction vessel by a vacuum pump system so that protection of the vacuum pump system from harmful materials can be quite important. The present invention, then, is directed to an apparatus and a method for removing the unwanted materials in the effluent whereby the effluent may be more easily handled by and less destructive to the pump system. This system is especially constructed to remove corrosive gases present in the effluents.
One example of a technology which may readily implement the present invention is the semiconductor fabrication industry. This industry is making increased use of low pressure operations such as plasma etching, plasma assisted deposition and the like. These processes require sophisticated vacuum pumping systems having expensive parts and often using expensive, inert pump oil. Since corrosive gases are utilized in these processes, the unreacted gases or the reaction by-products of these gases can be harmful to the pump system; it is thus desirable that they be treated prior to their passage into the pump mechanism. Presently, treatment of these unwanted materials is done in two ways.
Perhaps the most common technique and practice in the semiconductor industry utilizes a liquid nitrogen cold trap inserted into the gas line between the process reaction vessel and the mechanical vacuum pump system. By passing the process effluent through the cold trap, which is maintained at extremely low temperature, the gaseous additives and by-products are condensed before they reach the vacuum pump system where they would either react with its metal parts, thereby damaging the pump, become entrained in the pump oil or exit into the environment.
While liquid nitrogen cold traps enjoy widespread use, this technique of treating dangerous effluents nonetheless has several major drawbacks. One disadvantage is the high energy cost involved due to the extensive utilization of liquid nitrogen which, since it exists at a temperature of -196.degree. C., requires great expenditure of energy to produce. Another disadvantage is that, due to the regeneration time of the cold trap, it is necessary to use two traps for a single system so that they may be interchanged with one another whereby one of the traps is always "on line." This leads to inefficient equipment utilization and may double the cost of the by-product treatment system. A safety hazard exists in the cold trap systems since the trap concentrates the dangerous effluents. Any event which increases the temperature of the trap, such as a power outage or liquid nitrogen loss, may initiate an explosive chemical reaction. This danger is also present when the cold trap is regenerated since it must be warmed up prior to introducing new liquid nitrogen. Yet another drawback is that the materials condensed in the nitrogen cold trap still need to be neutralized; until they are neutralized, these materials remain dangerous to handle and to dispose.
A second common technique utilized to protect the mechanical pump system involves an approach wherein the mechanical pump system is made as an inert as possible. In such systems, all of the exposed pump parts are typically coated with Teflon, and inert pump oils and neutralizing filters are employed. In addition, the user regularly purges the oil system with high volumes of inert oil.
This second technique also has many drawbacks. For example, there is a substantial increase in the pump equipment cost since the parts must be Teflon-coated. Also, the cost of inert pump oil is quite high, costing hundreds of dollars per liter, so that a simple oil change may cost several thousand dollars. Another drawback is present since the pump system cannot be made truly inert; thus one who utilizes this technique merely reduces the frequency of major overhauls. Again, safety is a consideration since both the pump discharge and the pump oil can contain significant concentrations of the undesired and dangerous materials. Exposure to the oil during oil changes and the potential for oil spills both present potentially hazardous situations. Finally, as in the case with the cold trap, the oil must be treated to neutralize absorbed hazardous chemicals prior to disposal.
Accordingly, there is a significant need for an apparatus and process that can reduce or eliminate unwanted materials, such as corrosive gases, that may be present or produced during manufacturing processes or otherwise present in a gas flow line. There is a need for such a system that accomplishes the reduction of these hazardous materials in a more cost-efficient manner and that increases the safety of persons operating the system. The present invention addresses these needs.